Scott comes across an MS Paper on caching
Microsoft has just posted a very well written and informative guide to caching in ASP.NET.
In particular, Chapter 6 is a great read. Chapter 6, "Understanding Advanced Caching Issues" describes designing a custom cache. At first, I thought it was just going to be an overview, but upon further reading it looks like another application block. However, I could not find any mention of a code download.
This is something I have been thinking about/tinkering with for sometime now, so if possible I would love to see if I can get my hands on some of the code.